Depending on the back spacing used, you can fit a 31x10.50 on a 15x8 rim w/o issues. A 32x11.50 tire will rub at the body seam on steering wheel lock/under compression. Cutting or bending the seam over will fix the rubbing issue. A 2-3" body lift will clear 33's, but if you don't want/need a BL after the SA, there are other ways of clearing the larger tires.
With some 1.5" ball joint spacers, you could probably clear 33x12.50's, but would likely rub at full lock/compression, even w/the body seam mod. The spacers will give you 1.5" of lift, as well as a little more wheel travel.
You can also adjust the torsion bars, but that stiffens the ride and reduces the limited amount of up-travel the IFS has.
A combination of small lifts and modifications you can run 35's. I clear 35's on my '91 w/2" body lift, 1.5" ball-joint spacers, body seam modification, and cutting two inches out of the fender.
Power loss you are looking at about 11% w/31's, 15% w/32's, 18% w/33's, and 25% w/35's. You speedometer and mileage will also be off by the same amount, i.e, w/31's at 55mph on the speedometer, you are actually going 60mph. A lot of people don't mind the 10% w/31's, and some will tell you they are fine w/25% loss and 35's, but most swap gears for either 33's or 35's.
The IFS components are pretty strong, providing you wheel with what is between your ears and not the skinny pedal.
The main durability issue w/IFS is bent idler arms and knocking it out of alignment on the trail, both of which can be fixed/avoided/or set before heading home. I carry spare tie rod ends, and an idler arm, but have only needed one tie rod end. The CV's are strong enough for an open diff, however when running a front locker they can/do break. I carry two with me, but haven't broken one yet w/my front locker.